When molded into film or the like, ethylene/vinyl alcohol copolymers containing vinyl alcohol structural units in a high proportion exhibit excellent gas barrier properties, and hence they are used widely as packaging material. However, the ethylene/vinyl alcohol copolymers have such problems that they are liable to water absorption, poor in drawability as well as in heat resistance, and are difficult to mold at high temperature. In the molded articles obtained from the above-mentioned copolymers, there are such problems that they deteriorate in gas barrier properties on account of the water absorption properties of said copolymers, they are insufficient in impact resistance in a dry state and, moreover, they are poor in pinhole resistance.
On that account, the ethylene/vinyl alcohol copolymers as mentioned above are used singly rarely if ever and are used usually in combination with other materials. As an example of the combination use referred to above, there may be mentioned a multi-ply laminates prepared by laminating an interlayer composed of the ethylene/vinyl alcohol copolymer with other materials. Further, there have been proposed numbers of methods intended to obtain modified compositions by blending the above-mentioned copolymers and other resins. In the blending methods as mentioned above, however, it is difficult to obtain ethylene/vinyl alcohol copolymer compositions in which the defect of said copolymer has been removed markedly when the ethylene/vinyl alcohol is used as a main component of the resulting blend. On the other hand, when the resin other than the ethylene/vinyl alcohol copolymer is used as a main component of the resulting blend, it has heretofore been difficult to obtain compositions excellent in gas barrier properties owing to the ethylene/vinyl alcohol copolymer.
In recent years, there have been proposed molded articles excellent in gas barrier properties, said molded articles being obtained from ethylene/vinyl alcohol copolymer compositions prepared by blending ethylene/vinyl alcohol copolymers and other resins. For example, Japanese Patent Publn. No. 30104/1976 proposes molded structures having a stratiform structure and different in content of an ethylene/vinyl alcohol copolymer in the direction of thickness, said structures being obtained by molding a composition comprising polyolefin and ethylene/vinyl alcohol copolymers into a desired shape under specific conditions. Further, Japanese Patent L-O-P Publn. No. 121017/1980 discloses a stratiform molded article of polymer composition containing 60-95% by weight of polyolefin, vinyl alcohol (co)polymer and alkylcarboxyl-substituted polyolefin. The copolymers of polyolefin and ethylene/vinyl alcohol copolymers as disclosed in the publications cited above, however, are poor in compatibility and tend to become poor in moldability, and it is therefore not always easy to mold these polymers into thin-layer films, and the thin-layer films obtained, if any, are required to show a further improvement in gas barrier properties.
The present invention is intended to solve such problems involved in the prior art as mentioned above, and an object of the invention is to provide ethylene copolymer molded structures excellent in gas barrier properties, pinhole resistance and the like.
A further object of the invention is to provide ethylene copolymer compositions excellent in drawing properties, film-forming properties and heat stability at the time of molding thereof and, at the same time, excellent in gas barrier properties and pinhole resistance.